Method of drawing yarn using a plurality of separator rolls with each driven roll

ABSTRACT

A plurality of skewed freely rotating separator rolls associated with a driven yarn forwarding roll are positioned so that each handles one wrap of a multi-wrap threadline arrangement around the driven roll. The yarn or threadline contacts the surface of the driven roll in wraps of at least 150* in the first and last contacts with the driven roll and at least 30* on each intermediate contact.

O United States Patent 1 in] 3,890,422 Livingston 1 June 17, 1975 METHODOF DRAWING YARN USING A 2.956.330 10/1960 Pam 264/290 N PLU OF SEPARATORROLLS WITH 2,988,866 6/1961 Kleekamm et a1. 264/290 T l FQWICT et a11 1. 3,400,194 9/1968 Boone et a1... 264/290 T [75] Inventor: RichardDonnan Livingston, 3,471,608 10/1969 Schippers....,........i..........264/290 R Seaford, Del.

[73] Assignee: E. l. du Pont de Nemours &

' Primary Exammer-R0bert F. White Company Wilmington AssistantExaminer.1ames B. Lowe [22] Filed: Apr. 26, 1974 [21] Appl. No.: 464,368

Related US. Application Data 57] ABSTRACT [63] Continuation-in-part ofSer. No. 387,049, Aug. 9,

1973, abandoned.

A plurality of skewed freely rotating separator rolls [52] US, Cl264/290 R; 23/713; 264/D 73; associated with a driven yarn forwardingroll are posi- 425/131 17 tioned so that each handles one wrap of amulti-wrap 511 Int. Cl. B291: 17/02 headline arrangement around thedriven roll. The [58] Field of S h 264/290 210 F D[(} 73; yarn orthreadline contacts the surface of the driven 23 713; 425/ 1(] 17 131153 roll in wraps of at least 150 in the first and last contacts withthe driven roll and at least 30 on each [56] References Citedintermediate contact.

UNITED STATES PATENTS 2,883,733 4/1959 Notarbartolo el al. 28/713 3Claims, 3 Drawing Figures PATENTEDJUH 17 I975 SHEET FIG- FIG-

r1 mu PATENTEDJUN17 ms -,890.422

SHEET 2 FIG-3 1 METHOD OF DRAWING YARN USING A PLURALITY OF SEPARATORROLLS WITH EACH DRIVEN ROLL CROSS REFERENCE TO RELATED APPLICATION Thisis a continuation-in-part of my copending application Ser. No. 387,049,filed Aug. 9, I973 and now abandoned.

BACKGROUND OF THE INVENTION This invention concerns processing ofpolymeric fila ments and threads, more particularly, means forpositively controlling the elongation of such synthetic threads,especially when multiple threads are processed simultaneously.

Synthetic filaments and yarns are usually stretched after solidificationto increase their tenacity, stretching usually being accomplished bydriven rolls running at different speeds. Various means have beenemployed to prevent slippage of the yarn on driven rolls, such asemploying a series of driven rolls or an elastomer coated second roll.The least expensive method is usually a freely rotating roller locatedat a distance from and approximately parallel to the driven roller sothat the yarn may be wrapped more than once on the driven roller.However, subsequent wraps of the yarn must not touch previous ones ifabrasion and entangling are to be avoided. To accomplish this separationof sebsequent wraps, the axis of the separator roll is either canted orskewed with relation to the axis of the driven roll, canted meaning thatthe axes of the two rolls intersect when extended and skewed meaningthat the axes are not parallel and do not intersect. Cant is usuallyundesirable because the distance between the two rolls varies alongtheir length, requiring the yarn to stretch or retract, and yarns tendto slide erratically on the inclined roll surfaces. Skewed rolls,however, do not have these disadvantages if the yarn is positioned wherethe distance between the two axes is least. On the other hand, when verylong skewed rolls are employed, as when a single yarn is wrapped manytimes or when a large number of parallel yarns are handledsimultaneously, it can be seen that the distance between the axes of twoskewed rolls can be substantially greater than the minimum distance atthe end of the rolls. Thus, when a large number of parallel yarns arehandled simultaneously, the yarns on the extreme ends have a muchgreater tendency to slide or scuff than those at the middle. When suchinstability occurs, filaments may be transferred from one multifilamentyarn to another, giving finished yarns with the wrong number offilaments. In addition. such instability results in broken filaments andin variable degrees of drawing of the yarn.

When yarns are stretched between two rolls driven at different speeds,it is particularly important that slippage be minimized at each roll;therefore, the yarn should have a maximum possible degree ofwrap on theroll which it is leaving and the roll which it is approaching. This isparticularly important in so-called two-stage drawing where the yarn ispartially drawn in a firstdrawing stage and is drawn the remainder ofits ultimate draw in a second stage. The properties, such as dyeability,of the final product having a certain total draw may be quite differentdepending upon the proportion of draw taken in the first and secondstages. Therefore, it is important that all yarns of a multiple bundleshould be in stable contact with each roll so that all are treatedequally and uniformly with minimum abrasion,

A particular problem of using multiple wraps on a single separator rollcan be seen where undrawn yarn coming from the spinning operation iswrapped several times around a single separator roll associated with adriven feed roll. The tension in the filaments from the spinningoperation is low whereas the tension in the yarn leaving the feed rollis high as it enters the first draw zone. This high tension generallyresults in slippage of the last wrap so that the yarn on the last wrapof the separator roll tends to move forward while the yarn on the firstwrap of the separator roll coming from the spinning operation tends tolag. Thus, the yarn at opposite ends of the separator roll subjects theroll to conflicting tendencies and the separator roll speed may; varyerratically depending upon the degree of slippage and yarn stability.Such conflicting tendencies are particularly damaging when yarn passesover such a separator roll before its first contact with or after itslast contact with the driven roll.

SUMMARY OF THE INVENTION In a method for drawing synthetic yarn thatincludes passing substantially undrawn yarn in multiple spaced surfacewraps around a driven feed roll and a plurality of associated separatorrolls, then passing the yarn in multiple spaced wraps around a drivendraw roll and its associated separator rolls while maintaining the yarnbetween the feed and draw rolls at drawing tension, all rolls being ofconstant diameter, the axis of said separator rolls being skewed withrespect to the axis of said driven rolls, the improvement comprising:passing the yarn in multiple wraps around the driven rolls whilecontacting each of their associated separator rolls only once,therebeing one wrap on the driven roll for each associated separatorroll. The yarn or a band of parallel yarns is centered on the separatorroll at or near the point of closest approach of the axis of theseparator roll to the axis of the driven roll. Yarn contacts a separatorroll only after its first contact with a driven roll and before its lastcontact therewith. Preferably, the yarn or yarns wrap at least on thesurface of the driven roll at the first and last contacts therewith andat least 30 on each intermediate contact.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows synthetic yarn passingfrom spinning through two stages of drawing according to the method ofthe invention.

FIG. 2 is the right-hand side view of FIG. 1. FIG. 3 is an alternateembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1,multiple yarns 13, each consisting of a number of polymeric filaments,are extruded from spinnerets in spinning block 14 and are solidifiedbefore they reach guides 15 and 16 which keep the yarns separated fromeach other but closely spaced as they approach positively driven feedroll 17. The yarns contact feed roll 17 for an average wrap of about andthen pass via path 1 to freely rotating separator roll 18 which isskewed to advance the yarns as they approach feed roll 17 via path 2.They contact feed roll 17 for about 55 of wrap and then pass via paths 3and 4 around skewed separator roll 19 and back to feed roll 17. Theycontact feed roll 17 for about 35 of wrap and then pass via paths 5 and6 around skewed separator roll 20 and back to feed roll 17. They contactfeed roll 17 for slightly more than 180 of wrap and then pass via path 7to first draw roll 21 which is positively driven at a faster rate thanfeed rool 17 so that the yarns are partially drawn under drawing tensionmaintained between the two. The yarns contact first draw roll 21 forabout l60 of wrap and then pass via paths 8 and 9 around freely rotatingskewed separator roll 22 and back to first draw roll 21. Here they wrapabout 30 and pass via paths l and 11 around skewed separator roll 23 andback to first draw roll 21. They wrap on roll 21 for slightly more thanI80 and then pass via path 12 to a pair of second draw rolls 24 whichare positively driven at a faster rate than first draw roll 21. Theyarns are drawn additionally between first draw roll 21 and second drawrolls 24.

Since the speed at which filaments are removed from the spinneret isgoverned by the feed roll, it is important that maximum contact bemaintained between the yarn and feed roll during its first contact. Thearrangement of the invention permits an average wrap of at least 150around the feed roll at its first contact. The arrangement also allows awrap of at least I80 on the last wrap before the first draw zone. Theprovision of an intermediate separator roll 19 permits the first andlast separator rolls to be located in positions providing high degreesof wrap. However, high degrees of wrap are not necessary on intermediatecontacts between the yarn and driven roll as, for example, between paths2 and 3 and paths 4 and 5. It has been found that wraps of at least 30are desirable to prevent wandering of the yarns at such intermediatecontacts.

An additional advantage of the roll arrangement shown in FIGS. 1 and 2is that the yarn progresses in a single rotational direction, i.e.,clockwise, while being wrapped around the driven rolls and theirassociated separator rolls. A person stringing up such a machine canproceed more rapidly and with less chance of error if all wraps are madein the same direction,

If separator roll 19 is positioned so that yarn goes directly fromseparator roll 18 to 19 or separator roll 19 to 20 without contactingthe driven roll, the yarns become unstable. This may be partly caused bythe fact that such pairs of rolls may have opposite skews.

However, FIG. 3 shows one method of minimizing such problems. In thisalternative embodiment multiple yarns contact feed roll 17 for anaverage wrap of about I70 and then pass via path 1' to freely rotatingseparator roll 25 which is skewed to advance the yarns as they approachfeed roll 17 via path 2'. They contact feed roll 17 for about 100 ofwrap and then pass via path 3 to separator roll 26. The yarns then passvia path 4 to separator roll 27 and then back to feed roll 17 via pathThey contact feed roll 17 for about 180 of wrap and then pass via path6' to first draw roll 21 driven at a faster rate than feed roll 17. Theyarns Contact first draw roll 21 for about l60 of wrap and then pass viapath 7' to separator roll 28. From roll 28 they pass via path 8' toseparator roll 29 and then via path 9' to first draw roll 21. They wrapon roll 21 for about [60 and then pass via path 10' to second draw rolls(not shown).

Scuffing and instability of the yarns is minimized in the arrangement ofFIG. 3 because the yarns have a greater degree of wrap on feed roll 17between paths 2' and 3' than between paths 2 and 3 of FIG. 1, andbecause the yarns need to advance axially along feed roll 17 only oneband width in traversing paths 3', 4 and 5' and, therefore, the skewangles of rolls 26 and 27 can be smaller than those for rolls l9 and 20of FIG. 1.

Individual separator rolls for each wrap of yarn allow the yarn to seekits preferred speed. Thus, the elongation which the yarn may undergo inchanging from the low tension in the spinning zone to the high tensionof the draw zone can take place without affecting other portions of theyarn path. Similarly, when going from the first draw zone to the seconddraw zone in which the tension is higher, the yarn speeds may beslightly different between paths 8 and 9 and paths l0 and 11 due tocontrolled and minimized slippage.

It has been found that when large changes in tension and elongation insynthetic yarn occur, as in drawing the yarn, slippage or rolling ofyarn on a driven roll may be minimized through use of this invention.

Other arrangements of separator rolls than those shown in the drawingsmay fall within the present invention. For example, if the arrangementof other machine elements in FIG. 1 were such that yarn path 7 leavingfeed roll 17 were in a 10 oclock direction, sep arator rolls 19 and 20could be spaced between rolls 17 and 18 on a line between their centers.

What is claimed is:

1. In a method for drawing synthetic yarn that includes passingsubstantially undrawn yarn in multiple spaced surface wraps around adriven feed roll and a plurality of associated separator rolls, thenpassing the yarn in multiple spaced wraps around a driven draw roll andits associated separator rolls while maintaining the yarn between thefeed and draw rolls at drawing tension, all rolls being of constantdiameter, the axis of said separator rolls being skewed with respect tothe axis of said driven rolls, the improvement comprising: passing theyarn in multiple wraps around the driven rolls while contacting each oftheir associated separator rolls only once, therebeing one wrap on thedriven roll for each associated separator roll.

2. The method of claim I, the first and last wraps on each driven rollbeing at least with each intermediate wrap being at least 30".

3. The method as defined in claim 1, said yarn contacting each separatorroll once at the point of nearest approach of the axis of the separatorroll to the axis of the associated driven roll.

1. In a method for drawing synthetic yarn that includes passingsubstantially undrawn yarn in multiple spaced surface wraps around adriven feed roll and a plurality of associated separator rolls, thenpassing the yarn in multiple spaced wraps around a driven draw roll andits associated separator rolls while maintaining the yarn between thefeed and draw rolls at drawing tension, all rolls being of constantdiameter, the axis of said separator rolls being skewed with respect tothe axis of said driven rolls, the improvement comprising: passing theyarn in multiple wraps around the driven rolls while contacting each oftheir associated separator rolls only once, therebeing one wrap on thedriven roll for each associated separator roll.
 2. The method of claim1, the first and last wraps on each driven roll being at least 150*,with each intermediate wrap being at least 30*.
 3. The method as definedin claim 1, said yarn contacting each separator roll once at the pointof nearest approach of the axis of the separator roll to the axis of theassociated driven roll.